Low levels of vitamin D in the blood are associated with low mood. One explanation for the benefits of sun exposure on mood is that it increases blood levels of vitamin D. As vitamin D is required for proper brain function, this suggests that the benefits of sun exposure may be through its ability to normalise vitamin D status. However, while sun exposure on the skin increases blood levels of vitamin D, sunlight also improves mood, but may not necessarily have any effect on vitamin D levels. For example, it is known that hospitalisation for bipolar depression is reduced in length by increasing morning sunlight. However, this sunlight is effective if it is through a window and the person remains inside, thus removing the vitamin D factor. One explanation is that sunlight strikes the retinas and this causes modification to neuronal pathways in the brain. That light is able to cause these changes is not surprising as daylight length triggers all manner of biological changes in nature including changes to animals behaviour.
Evidence suggests there is an association between length of daylight and UV sun exposure and mood in cases of seasonal affective disorder. However, both the sunlight, and the sunlight’s ability to cause increases in vitamin D may be beneficial. There could also be synergism between the two factors in this case, such that both the daylight and the vitamin D are especially beneficial when they occur together.
Eat Well, Stay Healthy, Protect Yourself
RdB
